ATR and breast cancer: Candidate pathogenic mutations in untranslated regions (UTRs) and BC-relevant genes regions [18,19], including oncogenes (i.e., KRAS, ERBB3, PIK3C2G) and tumor suppressor genes (i.e., FANCC, ATR, SMAD2), were found in organoids, and the majority of them were conserved within the tumor–organoid pair (Figure 3b, Table S5).